Long-wave infrared detectors based on quantum wells have been found to be extremely responsive and efficient. The performance of such infrared detectors is close to that achieved with commercial mercad-detectors, i.e. mercury cadmium telluride-detectors. The wavelength response is a narrowband response, and can be selected between 3 and 15 micrometers.
Infrared detectors, IR-detectors, which use quantum wells are comprised of a thin layer of, e.g., gallium arsenide (GaAs) surrounded by aluminium gallium arsenide (AlGaAs). The most common type of IR-detector comprises 50 such quantum wells, each having a thickness of about 5 mm.
When infrared radiation of the correct energy impinges on the detector, electrons are excited to a state in which they can move readily from quantum well to quantum well, causing current to flow. The wavelength at which the detector has its maximum response may be varied intentionally, by appropriate choice of the dimensions and chemical composition of the quantum wells.
The most common detector is photoconductive. It is also possible, however, to manufacture photovoltaic detectors.
Quantum well detectors are either manufactured in accordance with the MOVPE-technique (metal organic gasphase epitaxy) or in accordance with MBE-technique (molecular beam epitaxy).
One serious problem common to quantum well detectors that are based on so-called intersub band transitions in the conductor band is that they are sensitive solely to IR-radiation whose electrical field vector has a component which is perpendicular to the quantum-well plane. This limits the degree of quantum efficiency and renders the majority of detector configurations sensitive to polarization. In particular, the detector is not sensitive, or responsive, to radiation which is incident perpendicular to the quantum-well layer.